Pulsed oil feeding system for industrial furnaces



' Nov. 23,1965 u. l. NILSSON 3,219,095

' Filed June 21, 1962 PULSED OIL FEEDING SYSTEM FOR INDUSTRIAL FURNACES 2 Sheets-Sheet l C I Q-ZH 007/ 0776 60/4 7 R,

15': I tn ti 1 E Nov. 23, 1965 u, N ss0 3,219,095

PULSED OIL FEEDING SYSTEM FOR INDUSTRIAL FURNACES Filed June 21, 1962 2 Sheets-Sheet 2 United States Patent C) 3,219,095 PULSED OIL FEEDING SYSTEM FOR INDUSTRIAL FURNACES Uno Ingvar Nilsson, Hoganas, Sweden, assignor to Aktiebolaget Hiiganiismetoder, Hoganas, Sweden Filed June 21, 1962, Ser. No. 204,287 Claims priority, application Sweden, June 22, 1961, 6,563/ 61 4 Claims. (Cl. 15836) In oil-fired industrial furnaces, such as annular furnaces and chamber kilns for firing bricks and other ceramic burning and sometimes also in tunnel kilns, it is common practice to provide each furnace with a plurality of oil burners which intermittently inject the oil into the firing kiln. It has proved advantageous to inject the oil in the form of intermittently discontinued jets which strike upon a wall or impact projections where they are atomized and ignited. These oil jets can be directed to predetermined places in the furnace chamber. ,As a result of the temporary shortage of oxygen in the zone surrounding the jet just ignited there is obtained a long and soft flame which preserves the material to be heated and ensures a favourable and uniform distribution of heat. The oil burners usually inject the oil at a pulse recurrence frequency chosen in dependence upon the furnace and local conditions. In hitherto known pulse firing systems the burners are provided either with built-in pulse valves which are controlled by the shock waves in the oil supply duct or with built-in electromagnetically driven pumps controlled by current pulses from a common control apparatus. Consequently, in both types of systems there is provided a common control apparatus which emits hydraulic or electric control pulses to all or at least most of the burners of a furnace such that the intermittent oil injection takes place simultaneously through all of the burners. As a result, shock waves are generated in the furnaces, this being, of course, rather disadvantageous. In addition, burners provided with individual oil pumps or hydraulic fluid-controlled valves or the like are very sensitive to air in the oil and sometimes also to the temperature responsive viscosity of the oil. Further, the use of an intensely pulsating pressure in the oil supply ducts of the burners is disadvantageous on account of the fact that flexible tubes and pipes as well as the appertaining couplings are subjected to high stresses and that the pressure pulses get mixed up, since the pressure gradients are considerably impaired by longer and not sufficiently unelastic rigid ducts. Since the conventional electrically controlled burners for intermittent injection of oil act as individual electromagnetically driven pumps, the electrical power required is rather high and amounts to about 100 watts or still more for each burner. As a result of the rather great number of burners and their low control voltage of usually 24 volts the control current conductors and the common control apparatus have to be amply dimensioned.

In the above-named furnace systems the amount of oil per impulse is individually adjusted for each burner by means of a control screw or the like. This procedure is complicated and often unsuitable and requires a timewasting supervision. Usually, the furnace has but one or a few inspection windows. For this reason, supervision and control are to be performed, as far as possible, at one of these places.

Further, it is often required that the burners, or still better complete groups of burners with appertaining control members, oil ducts and so on should be able to be conveniently shifted between the individual furnace chambers, which means that the burners and accessories should be light and of small sizes. In certain conventional systems, they are too heavy so that they cannot be comcated remote from the burner for electric remote control of the burner, and the invention is characterized in that said valve is a solenoid valve, preferably a needle valve. the movable part (needle) of which has a small mass and a short length of movement, and that the pulse transmitter is an adjustable pulse transmitter, preferably a multivibrator with adjustable duration and/or recurrence frequency of the pulses, the output of the pulse transmitter being directly connected to the coil of the solenoid valve.

As a result of the low electric power consumption of the movable part or needle of the valve and due to the small mass and short length of movement, the valve is able to operate with short pulses, low pulse power and a comparatively high pulse recurrence frequency. Besides, wear is reduced to a minimum.

In view of the extremely low power consumption it is possible to control all of the burners by individual electronic pulse generators or pulse transmitters. Consequently, the pulse transmitter may be devised as a transistor multivibrator the duration and recurrence frequency of the pulses of which are adjustable such as by means of ordinary turning knobs or similar members which may be provided for each individual burner or may be common to a group of burners or all of the burners. It is possible and in most cases suitable to vary the duration and recurrence frequency of the pulses by means of a single control member, such as a turning knob, and a special circuit is provided for this purpose resulting in the advantage of a very large adjustable range of amount of the injected oil (time integral of the oil amount, but not oil amount per pulse). In addition, this oil amount can be varied if the burner nozzle is replaced by a nozzle having a different cross-sectional injection area. Consequently, the burner is universally usable, it being possible by replacement of the nozzle to choose a desired wide range of operation or range of coarse adjustment for the stepped or continuously variable fine adjustment, that is, for the control of the duration and recurrence frequency of the pulses. It is also possible to obtain an approximately logarithmic relation between the angular setting of the knob and the amount of oil, resulting in a constant percental variation of the amount of oil upon a given angle of setting independently of the position of the knob. The pulse transmitter is small and light and can be located at any suitable place with respect to the appertaining burner.

It is suitable to combine a plurality of burner units for a furnace chamber in a readily portable frame and to as semble the individual pulse transmitters appertaining to these burners in a common control box which may be suspended at a suitable inspection window of the furnace. The burner frame and the control box are interconnected by means of a multiple-conductor cable having easily disengageable connections, such as multiple pin and plug sockets, such that the entire equipment can be readily shifted to another place. For instance, the control box can be connected by means of an ordinary contact plug to any one of the Wall sockets of the mains, since the total current consumption need not exceed about 2 watts per burner. of the pulses of each burner is entirely individually ad-, justable by means of such a centrally located control boX.

The recurrence frequency and/ or duration Without variation of the just mentioned adjustment it is possible to shut off the injection of oil to a whole group of burners by means of a switch provided at the control box, for instance in order to be able to observe fusible cones or to take temperature measurements by means of an optical pyrometer. Since the pulse transmitters operate independently of each other, that is, non-synchronously, and often are adjusted for different pulse recurrence frequencies, a very uniform firing process will be obtained in the furnace.

As already mentioned, it is of great importance to have a low electric control power for the solenoid valves. A conventional solenoid-driven pump for intermittent oil injection requires for each burner a control power of more than 100 watts during the pulses, and, in addition, a greater number of burners are to be controlled simultaneously requiring a correspondingly higher .total power. Consequently, at the low control voltage of normally 24 volts and with the usually great number of burners the current will be of high intensity and the control current conductors, such as copper bars, and the installation thereof will be correspondingly expensive. This also holds true of the common control box and the construction thereof.

An embodiment of the invention is described hereinbelow with reference to the accompanying drawings. FIG. 1 illustrates a burner with a solenoid valve and connections for fuel oil and current. FIG. 2 is a circuit diagram of an adjustable pulse transmitter, and FIG. 3 is a diagrammatic view of eight burners assembled in a portable frame together with eight pulse transmitters assembled in a portable box.

FIG. 1 illustrates a suitable burner the control of which requires an electric power of only slightly more than 1 w. (555 ma. at 22 v. or a pulse power of 1.2 w., the continuous mean power varying between 0.04 and 0.07 w. according to the adjustment). The burner head 1 comprises a nozzle 2 for the injection of a jet of fuel oil. Behind the nozzle there is provided a seat for a valve needle 3 the end of which remote from the seat is in the form of a solenoid armature 4. If desired, the rearward part of the nozzle may form the seat. A spring 5 biases the needle 3 to the seat so that the valve is normal-1y closed. An external sleeve or shell 6 of the burner houses a coil 7 which surrounds a core 8. This core as well as the sleeve 6 and two partitions 9 and 10 consist of a magnetically soft material, such as soft iron, and form a magnetic circuit having a coaxial non-magnetic air gap 11. This gap is preferably filled with a non-ferromagnetic material having a downwardly directed projection 11 to prevent butt contact with consequent magnetic adhering of the armature of the valve needle. The coil 7 has a cable connection 13 which extends outwards through the connecting piece 30. The burner also comprises a connecting piece 12 for a flexible oil supply tube 31. This connecting piece houses a magnetically as Well as mechanically operating oil filter 32 and communicates through a bore 33 in the burner head with a cavity 34 above the valve seat. If current is supplied to the coil, the valve needle 3 is pullled upwards against the action of the spring 5 and opens the nozzle for the oil.

FIG. 2 illustrates a pulse transmitter according to the invention. The output of the pulse transmitter is connected to the coil 7 of a burner as indicated on the drawings. It comprises transistors in a special multivibrator circuit of low frequency. The multivibrator itself consists of two transistors T and T with appertaining circuit elements. The emitter of the transistor T is connected with the base of an output transistor T which controls an electromagnetically operated solenoid valve and a signal lamp L. A fourth transistor T is comprised in the circuit in the form of an emitter follower and amplifies the charging pulses of a condenser C This additional amplification isdesirable or necessary in view of the comparatively low frequency of the multivibrator and the consequent high capacitance (about 32 mircrofarads) of the condenser C As shown, the multivibrator is unsymmetrical, and the duration of the pulses generated thereby can be varied continuously by means of a resistor R The pulse recurrence frequency or more exactly the spacing of the pulses is continuously variable by means of another resistor R However, in most cases it is suitable to replace the two resistors by a potentiometer, as shown in FIG. 2, so that upon displacement of the potentiometer tap, such as by means of a turning knob (not shown), the resistance of R will be increased and the resistance of R decreased, and vice versa. Since the amount of oil injected by the burner is proportional to the duration as well as the recurrence frequency of the pulses, a very wide control range is obtained in this manner for the amount of oil injected into the furnace per unit of time. With the values of the various circuit elements indicated in FIG. 2 the duration of the pulses is continuously variable between 0.1 second at a frequency of 20 pulses per minute and 0.4 second at pulses per minute, responding to a control range of the duration of injection integrated with respect to time of about 3 to 60%.

The output transistor T supplies current to the signal lamp L as well a the solenoid valve of the appertaining burner. By way of example, the lamp L may be devised for a service voltage of only about 10 volts and connected via a corresponding series resistor R Due to this arrangement, the otherwise high transient switchingon current for a cold filament is avoided, and the output transistor T is protected from the high current tops which otherwise would occur for each injection pulse. Even the smallest conceivable signal lamp has a current consumption which by no means is negligible as compared with the consumption of the solenoid valve, and it is therefore undesirable to have to overdimension the pulse transmitter merely because of the peak loads occurring as the signal lamp is repeatedly switched on, such overdimensioning being avoided by the above indicated measures. The magnet coil is shunted by a rectifier 35 which is directed such as to be practically nonconductive in the direction 'of the control current, but short-circuits the inductive current pulses occurring during pulse operation and consequently protects the output transistor from these pulses.

If the circuit of the pulse transmitter is in the form of a printed circuit it can be made small and light so that a control box housing a plurality of such pulse transmitters requires a space of less than about 30 cubic inches per pulse transmitter. Preferably the control box also house a small mains equipment together with a transformer and rectifier for converting 220 (or volts A.C. into 24 volts D.C. having an input power of about 2 watts per pulse transmitter. The control box together with its contents is fairly light and requires a small space only and can be conveniently carried from one kiln chamber to another one when the burners connected thereto are shifted. The control box can be directly connected to the wall socket of the mains. On the front side of the control box there are provided one or two knobs 36 and signal lamps 37 for each burner. An important advantage consists in the possibility of convenient supervision of the control box and, consequently, the function of the oil burners due to the fact that the signal lamps are lighting and extinguishing in rhythm with the solenoid valves of the burners. It is thus possible to observe at every moment the operation of each individual burner and the cooperation of the various burners, this being important if the rhythm of operation of one or more burners is varied by means of the knobs.

If a greater number of burners are used per furnace and the various groups of burners must be able to be easily shifted, such as in case of a travelling heating zone in annular and chamber furnaces, the burners are preferably arranged as illustrated in FIG. 3. A certain number of burners corresponding to a certain heating zone are assembled in a frame 14. The frame is provided with holders for the burners to be shifted and comprises two longitudinally extending pipes 16, 23 which preferably constitute a bearing member for the frame and serve as a supply pipe for fuel oil and a protective or armoured pipe, respectively, for the electric conductors. For each burner the oil supply pipe 16 has a fitting with a cut-0E cock 17 for the oil. By means of flexible tubes 18 each of the fittings can be connected to one of th burners 19. By means of a flexible tube 20 and a quick coupling 21 the pipe 16 communicates with an oil supply conduit 22 provided above the furnace.

The pipe 23 of the frame has control-current conductors with terminals 24 (preferably plug bushes or the like) for the supply cable of each burner to be connected.

A flexible multiple-conductor cable 25 is by means of a multiple contact plug 26 or similar member connected to all of the terminals 24 and to a control box 27 which house all of the pulse transmitters appertaining to the group of burners. By means of an ordinary lamp cord 28 the control box 27 is connected to a wall socket 29 of the mains.

To shift a burner group it is merely necessary to insert the burners into the respective holders 15, as shown for the first five burners to the left in FIG. 3, whereupon th oil duct coupling 21 and the contact plugs 26 and 29 are released. Then, one man can easily carry the burner frame together with the burners and the control box 27 to another place, since these portable parts are sufficiently small and light.

In a heating system of the kind described in which a plurality of burners are assembled or combined to a group of burners it may be suitable automatically to control one of the variable magnitudes of the pulse transmitters, preferably the duration of the pulses, by means of a temperature indicating device which is located in the heating zone provided with the burner group and which is provided with a control common to all of the burners of the group. The second variable magnitude of the pulse transmitters, preferably the pulse recurrence frequency, is suitably controlled manually and individually for each burner.

What is claimed is:

1. A fuel burning system for heating industrial furnaces with liquid fuel comprising a plurality of burner units, each unit comprising a burner having a needle valve located in the fuel supply duct thereof, said needle valve being of relatively small mass and having a short path of movement, a solenoid and a spring positioned respectively to open and close said needle valve and a plurality of remote multivibrators each having its output directly connected to the coil of one of said solenoids, each multivibrator comprising associated control means for varying at least the recurrence frequency of the output pulses thereof to control the operation of the burner, said multivibrators and their associated controlmeans being mounted as a portable unit.

2. A fuel burning system as claimed in claim 1 in which each multivibrator is so controlled by said control means that an increase of the pulse duration necessarily involves an increase of the pulse recurrence frequency, and reversely, so that a large region of adjustment of the product of pulse duration and recurrence frequency is obtained.

3. A fuel burning system as defined in claim 1 in which all of the multivibrators and their associated control means are mounted upon a portable unitary structure, said system comprising a common control member mounted on said structure for controlling the pulse duration and the pulse recurrence frequency of each multivibrator.

4. A fuel burning system as claimed in claim 1 in which a temperature-sensing means is associated with a heating zone to be heated by said plurality of burner units and controls the pulse duration of the output pulses of said multivibrators in dependence on the sensed temperature, and wherein each of said control means controlling the recurrence frequency of said output pulses of the associated multivibrator is manually adjustable.

References Cited by the Examiner UNITED STATES PATENTS 2,577,853 12/ 1 Kurata 15 877 2,582,331 1/ 1952 Hoetfken 158-2 2,646,931 7/ 1953 Suter 236-49 2,907,382 10/ 1959 McIlvaine 15 8-77 2,933,051 4/ 1960 Toulmin 103--5 3 2,982,530 5/ 1961 Drakengren 15 877 2,987,293 6/1961 Knudson 158-77 3,070,024 12/ 1962 Rornberg 1035 3 3,090,423 5/1963 Garner et al 251-429 X FREDERICK L. MATTESON, JR., Primary Examiner.

PERCY L. PATRICK, JAMES W. WESTHAVER,

Examiners. 

1. A FUEL BURNING SYSTEM FOR HEATING INDUSTRIAL FURNACES WITH LIQUID FUEL COMPRISING A PLURALITY OF BURNER UNITS, EACH UNIT COMPRISING A BURNER HAVING A NEEDLE VALVE LOCATED IN THE FUEL SUPPLY DUCT THEREOF, SAID NEEDLE VALVE BEING OF RELATIVELY SMALL MASS AND HAVING A SHORT PATH OF MOVEMENT, A SOLENOID AND A SPRING POSITIONED RESPECTIVELY TO OPEN AND CLOSE SAID NEEDLE VALVE AND A PLURALITY OF REMOTE MULTIVIBRATORS EACH HAVING ITS OUTPUT DIRECTLY CONNECTED TO THE COIL OF ONE OF SAID SOLENOIDS, EACH MULTIVIBRATOR COMPRISING ASSOCIATED CONTROL MEANS FOR VARYING AT LEAST THE RECURRENCE FREQUENCY OF THE OUTPUT PULSES THEREOF TO CONTROL THE OPERATION OF THE BURNER, SAID MULTIVIBRATORS AND THEIR ASSOCIATED CONTROL MEANS BEING MOUNTED AS A PORTABLE UNIT. 